The current invention relates to a trigger in a paint spray gun which opens a valve by pushing the valve against the pressure of a fluid, the fluid being either a liquid or a gas.
Paint can be applied evenly over a surface by being atomized by a paint spray gun. In the prior art, as shown in FIG. 1, a paint spray gun 10 atomizes paint found in container 12 by pulling the paint into a stream of air. Pressurized air enters the gun 10 through coupling 14 and passes through a hollow handle 16 into a preliminary air chamber 18. When trigger 20 is pulled, the trigger 20 pivots about pivot point 22, urging an actuator 24 rearward. The actuator 24 may be attached to trigger 20, or may merely abut trigger 20 without being physically attached. When the trigger 20 is released, a spring 25 urges the actuator 24 forward and the trigger 20 returns to the rest position shown in FIG. 1. The actuator 24 is effectively a stiff rod attached to an air valve 26 which serves to regulate the passage of air from preliminary air chamber 18 through the remainder of the gun 10. As actuator 24 moves rearward, the air valve 26 is also moved rearward away from valve seat 28. This movement pushes the valve 26 against the pressure of the pressurized air in preliminary air chamber 18. As a result of this pressure, a significant amount of force is required on the trigger 20 to move the valve 26 away from seat 28. However, once the actuator 24 has opened the valve 26, the pressurized air passes into air passageway 30, thereby substantially equalling the pressure on both sides of valve 26 and making the movement of the valve 26 easier. After the pressurized air enters passageway 30, it moves through air passageways 32, 34 and 36. Passageway 36 is in communication with a recess 38 in an air cap 40, thereby allowing the pressurized air to pass through recess 38 and exit gun 10 through an opening 42 in air cap 40. The volume of air exiting the gun 10 through opening 42 affects the characteristics of the atomized paint stream created by the gun 10. This volume is controlled by an air control mechanism 60.
When the trigger 20 moves the actuator 24 rearward, a needle end 50 of actuator 24 also moves rearward, thereby opening needle or paint valve 52. This allows paint in container 12 to pass through paint passageways 54 and 56 and to exit the gun 10 through paint valve 52. The passage of air through opening 42 acts to suction the paint out through paint valve 52 when paint valve 52 is open. When the paint exiting valve 52 enters the stream of pressurized air, the paint is atomized, thereby allowing the paint to be applied to a surface.
As the trigger 20 pushes the actuator 24 rearward, the actuator 24 first opens air valve 26 and then, after further rearward movement, opens paint valve 52. In order to open paint valve 52 fully, the actuator 24 must move rearward a significant distance relative to the distance required to open air valve 26. Thus, the trigger 20 must not only move the actuator 24 against the pressurized air to open air valve 26, but then must move the actuator 24 a sufficient distance so as to allow the operator to control the amount of paint exiting paint valve 52.
Unfortunately, this places two conflicting requirements on the design of trigger 20 and the placement of pivot point 22. Since a significant amount of force is required to unseat valve 26 from seat 28, it is useful to place the pivot point 22 relatively close to actuator 24. This would create a significant mechanical advantage in the trigger 20, making it easier for an operator to start air flowing through gun 10. On the other hand, since it is important to allow an operator to control the volume of paint passing through paint valve 52 during usage of the gun 10, it is helpful to have the pivot point 22 relatively far from the actuator 24, thereby allowing greater control over the amount of paint being sprayed.
A similar conflicting need is found in airless spray guns, where pressurized paint is atomized by forcing the paint through a paint nozzle at a high pressure. In these guns, the trigger must force a paint valve against the pressure of the pressurized paint. After opening the valve, the trigger must move the valve a significant distance from the seat in order to minimize paint flow resistance.
The present invention meets these dual needs by providing a trigger with two pivot points. The first pivot point is close to the actuator and is used while the trigger moves through a first range of motion. The location of this first pivot point increases the mechanical advantage of the trigger, thereby making it easier to open the valve against the fluid pressure. The second pivot point is further from the actuator and is used while the trigger moves through a second range of motion. The location of the second pivot point provides operation of the trigger at a decreased mechanical advantage thus increasing the distance travelled by the gun's actuator and valves in the second range of motion.